Hi Mike,
I have at last managed to wade through ‘The Role of Decoherence in Quantum Theory’. Did you post this as a joke? It reads like an essay in Post-Modernism. I have never heard the term ’Decoherence’ before, but it sounds like things falling apart, with the inevitable result of ’Incoherence’. My spell-checker doesn’t like it either. I suggest you choose references from an Encyclopaedia of Science rather than an Encyclopaedia of Philosophy! I checked it all out in my 'Feynman Lectures', published in 1961, and it was all there expressed in simple english.
Decoherence is now a proper proper physics term, honest. You can see references to it in all sorts of physics publications e.g:
Page not found | American Institute of Physicshttp://www.physics.uiuc.edu/...hlights/entangled-photons.htmhttp://physics.nist.gov/MajResProj/QuantumInfo/quantum.htmlHome – Physics Worldhttp://www.uni-protokolle.de/buecher/isbn/3540411976/
I wasn't making the word up! Does your spell checker like the word "inflaton", or "hadron" or "p-brane"?
You're right though, I saw you're initial question, thought to myself "decoherence", googled it, saw an article that covered it in some depth which I skimmed and was going to use in an answer to you and then ran out of time, so posted the link instead. With the benefit of hindsight, I would instead have posted the link I posted in a later message:
The Everett Interpretation
which is less clunky and more relevant. My apologies if you felt your time was wasted - I don't think the article I originally linked to was that bad though.
So I guess its incumbent upon me to attempt more explanation this time and less linking. I'm not an expert and all my info comes from reading non-technical books and articles, but I'll give it a go:
Firstly, I can see two possible processes of ‘splitting’. Either the whole universe splits apart in one go, or the else split initiates in that volume where the collapsing quantum field had a non-zero amplitude, and then propagates over the rest of the universe at the speed of light. This latter process could be likened to spreading two sheets, one on top of the other, and then lifting the top one at its centre. The separation spreads outwards in a circle.
I don't really understand what you mean by a parallel universe propagating at the speed of light. What's propagating through what?
My take on it is to imagine Schrodinger's cat, set up the experiment as normal and then throw out the cat and put yourself in the box. According to your assistant outside the box (who subscribes to the Copenhagen interpretation), you are in a state of quantum superposition, 50% alive and 50% dead. According to the many worlds interpretation you are either dead or alive. I'm pretty confident that either dead OR alive other would accord with what you experience, so of the two its only the MWI which allows for a sharply defined version of what we can describe as reality, in terms of agreement between different observers.
With MWI, a universe branches off everytime a new measurement is made - e.g on the two slit experiment the universe branches off once the photon hit the detector, with all physically allowable possibilities being realised. In fact the only rational explanation for single photons building up an interference pattern which is dependent upon the paths available to it must indicate that the photon is interfering with another photon somehow. The MWI provides all the necessary predictive power that QM has without any of that pseudoscientific mumbo jumbo about a conscious observer or the nature of reality being "mysterious".
In the first case, our local space is being split continuously by ‘quantum collapses’ that occur all over the universe. If the universe is infinite, we have an infinity of splits at every instant.
In the second case, we have splits arriving here all the time, from events in distant space and time. For example, an electron being absorbed by a molecule somewhere in a distant galaxy a thousand million years ago! In this case the number of splits may not be quite infinite if the universe has a finite past - but what difference will it make?
I'd agree with the first case and not sure about the second case. We can only observe the Universe we're in. This may sound tautological, but the chances are that we're in a Universe which is in no way out of the ordinary.
Its only recently that MWI vs Copenhagen has moved from a pithy and fruitless debate between philospophers and renegade physicists to growing speculation that it might actually be testable, of which quantum suicide is probably the most outlandish (and my favourite) example.
Well, actually there's an extension of this that say's imagine there was a freakishly bizarre quantum event which stopped you from dying at the very moment you would normally die in the majority of universes. In at least one universe these freakish events would continue to be experienced by you again and again and again....you'd never die. So, the argument goes, if the MWI is accurate, we are ALL effectively immortal. Personally, I can't see the flaw in the logic here although even Tegmark himself doesn't go this far. I'm not about to go jumping off any roofs to test it out just yet though.
That bullet goes through your head in an infinity of infinities of universes, and it doesn't go through in another infinity of infinities of universes. Which infinity is greater?
Well that's the nub you see - the whole point of the experiment. Let's simplify it a bit and say there's a 99% chance of you dying.
So in 99% of all universes you are no longer conscious of anything, your assistant is left to scoop your quivering brain matter off the floor.
In 1% of universes you are still conscious, albeit slightly soiled.
The key here is realising that what is it that YOU experience as you undergo the experiment will always be the 1% of cases - how could you possibly
experience anything else?
Hope that was clearer. Sorry once more for the duff link.
PE
This message has been edited by Primordial Egg, 09-07-2004 07:00 PM
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